User feedback channels were enabled from the get go - no point in interating your product development if the underlying foundation is already disliked, and you can't know if it is unless you are getting feedback from your alpha/beta testers.
In https://employplan.com we've had a Slack channel since the very first users. User feedback is the best way to determine the way you should develop your software (not in all cases of course). Also even the brightest UX designer won't prepare flawless design: it's very important to get rid of any bugs or holes as soon as possible.
You don't need a discord or slack though. Simple "let us know what you think" with a email provided may be a source of a great feedback. ;)
We were asking users individually at the beginning. Now that we're working on the second version of our product, we're using canny.io to get feedback on elements such as new features & bugs.
I think it's more about an ongoing process that trying to shoot for the "right moment". If you have an MVP, then I would build specific milestones: First 10 users, first 50, first 100, etc. Afterward, it's about having a process to get ongoing feedback but at first, I think it's very important that you listened to your customers.
Have a feedback channel set up and ready to go before you push that beta or MVP - you need feedback *early* to ensure you're on the right track. Fair warning - don't jump on every request for a feature or a change if it will delay an upcoming update. But if you get enough similar feedback, then you should put it on the product roadmap.
DO acknowledge the feedback you get. You might want to create a specific #wishlist channel, as well as one for generalized support and non-feature feedback.
Use https://beamdock.com. It's a free portal where your request can request for a feature, add feedback or even upvote an already created feature/feedback. Your users also get to schedule a User Interview automagically, if that's a part of your current product management workflow. There are a lot of other features, happy to discuss this over a call and understand your use-case.